The present invention pertains generally to the field of antennas and antenna systems for wireless communication devices (WCD). In particular, the present invention relates to a PIFA-edge antenna and an omnidirectional diversity antenna system which exhibit improved wireless data transmission and reception for portable wireless communications devices, such as xe2x80x9claptopxe2x80x9d computers, coupled to a computer network such as a wireless local area network (LAN).
Prior art wireless communication devices have constantly strived toward improved performance while following the continuing trend toward lower cost, and ever more compact antenna designs. In wireless LAN data transfer operations, loss of signal strength, interruptions in a data transfer, and the well known deleterious effects of signal interference, including phase cancellation and polarization rotation due to multiple surfaces reflecting RF signals, all present potential sources of error during data transfer which must be reduced if not eliminated altogether so that the wireless LAN exhibits a level of stability and error-free operation approaching that of known hard-wired LAN computing and communication environments.
One related approach to the significant problem of multiple surfaces reflecting RF signals in an office environment (known as multipath propagation interference) is disclosed in U.S. Pat. No. 5,677,698 entitled, xe2x80x9cSlot Antenna Arrangement for Portable Personal Computers,xe2x80x9d which issued on Oct. 14, 1997 to Snowdon. This related approach discloses two orthogonal slot antennas on the rear surface of a laptop computer that provides a modicum of polarization diversity for vertical and horizontal polarized RF signals only when the cover, or lid, of a laptop computer is oriented in the raised position. Thus, any advantages provided by this related antenna system only apply during the brief amount of time over the operating life of laptop computers outfitted with the antenna system disclosed that the cover is open. Thus, there exists in the related art a known obstacle to reliable operation of a wireless LAN system; namely, multipath interference propagation effects.
Local area networks (LAN) are used in the wireless transmission and reception of digitally-formatted data between sites within a building, between buildings, or between outdoor sites, using transceivers operating at frequencies in the range 2.4-2.5 GHz., 5.2-5.8 GHz., and others. Antennas operating over these frequency bands are required for the transceivers in LAN devices. A LAN structure permits many computerized devices to communicate with each other and/or with other computerized devices associated with the LAN. These other computerized devices may comprise such things as computer servers linked by optical or traditional electrically conducting conduit(s) to remote locations via a global computer system (e.g., the so-called internet or world wide web) as well as portable computers and personal digital assistants locally coupled to the LAN. In addition, peripheral computer equipment are often electronically coupled to the LAN either directly with conduit or using wireless network technology (e.g., RF transceivers). These peripheral devices typically include printing equipment, scanning equipment, photocopy equipment, facsimile transmission equipment, and the like. Individual stations, or nodes, of a LAN may be randomly positioned relative the other stations in the LAN without regard to sources of multipath propagation interference. Thus, as exhibited in the prior art, a need exists to provide continuous, reliable access to all the devices coupled to a wireless LAN including the need for simple, low cost, and effective antenna systems to combat the ever present effects of multipath propagation interference. Accordingly, continuous improvement in the operation and packaging of omnidirectional antenna assemblies enhance operational performance of a wireless LAN and are desirable for transceiver units disposed in computerized devices coupled to a wireless LAN. Unfortunately, a significant drawback of omnidirectional antenna designs is the susceptibility to multipath propagation interference which reduces RF signal strength by phase cancellation, often resulting in unacceptable errors during data transfer operation when digital information is being transferred over a wireless LAN.
In many wireless systems it is desirable to employ some form of antenna diversity to combat multipath effects in the communication system. The antenna diversity can be accomplished via several approaches, as known and used in the prior art; namely, frequency diversity, time diversity, spatial diversity, and polarization diversity.
Frequency diversity refers to a technique whereby an antenna system rapidly alternates among several different frequencies within a desired operating band of frequencies to reduce multipath propagation interference by simply spreading data being transferred in a wireless LAN over discrete portions of a usable frequency bandwidth which naturally avoids interference between diverse frequencies.
Time diversity refers to a technique whereby radio-frequency (RF) data transmission and receipt are timed to occur when only a single signal is being transmitted or/or received at a time over a wireless LAN, thereby simply avoiding the potential for plural RF data signals from interfering with each other by carefully controlling each transmission and reception operation.
Spatial diversity refers to a technique whereby two or more antennas are strategically placed at physically different locations to reduce multipath propagation interference during data transfer transmission and receipt.
Polarization diversity refers to a technique whereby data transmission and data receipt are provided at a common frequency but having distinct signal polarization such as vertical polarization, horizontal polarization, or polarization upon a pre-selected azimuth (expressed with values having a magnitude between 0 degrees and +/xe2x88x9290 degrees).
Many prior art systems use a pair of patch antennas to form a spatially diverse antenna configuration. Such an antenna may be formed on a resin-based, ceramic, or other suitable dielectric substrate. A typical patch antenna includes the substrate, an electrically conducting patch member formed on one surface of the substrate, and a ground plane disposed on the opposing surface of the substrate. A via aperture, or other electrically conducting feed pathway, electrically couples the electrically conducting patch to an RF receiver/transmitter (i.e., transceiver). The use of high dielectric constant materials for the substrate results in an antenna which is physically small, especially when a ceramic substrate is utilized although such ceramic-based substrate patch antennas tend to be relatively expensive. Furthermore, connecting the antenna to a low cost circuit board often requires special connectors and cabling, which add cost to the system.
The present invention teaches, discloses and enables those of skill in the art of wireless communication device (WCD) design and implementation to practice a PIFA-edge antenna and a novel diversity antenna system operable over a wide range of conditions and exhibiting superior performance as part of a wireless LAN environment. The antenna system of the present invention provides reliable and consistent omnidirectional performance while reducing the deleterious effects of multipath propagation interference which is often present in office environments having a variety of surfaces that passively reflect a broad range of frequencies useful within the broad spectrum the electromagnetic radiation (e.g., radio frequency or xe2x80x9cRFxe2x80x9d) for transmitting analog or digital voice, data, images, and the like (herein xe2x80x9cdataxe2x80x9d) typically transmitted across the typical LAN.
In particular, the present invention teaches a polarization and spatial diversity antenna system suitable for use with a laptop computer, hand-held device such as a so-called personal digital assistant (PDA), or other new, emerging, diverse and/or reasonably foreseeable wireless device networks. Examples of such wireless devices include those designed to operate in a single wireless data environment or in combination with one or more discrete wireless data environment. Such wireless environments can be locally based, such as a LAN in a business, residential, or vehicular setting, including land, sea, and air vehicles. Another variety of wireless data environments benefiting from the teaching of the present invention include those with greater reach or having a wider coverage area, such as a wide area network (WAN), satellite and low power space-based wireless data environments.
The present invention also teaches, discloses and enables those of skill in the art of wireless communication device (WCD) design and implementation to practice a novel PIFA-edge antenna operable over a wide range of conditions and exhibiting superior performance. The PIFA-edge antenna according to the present invention is a low-profile antenna exhibiting generally equivalent performance as compared to other, generally larger, PIFA antennas. In a PIFA-edge antenna according to the present invention, the distance between the planar element and the ground plane is substantially smaller than other antennas having similar performance characteristics. The provision of an additional grounding leg facilitates a more compact, low profile antenna.
The antenna system of the present invention finds optimal use in many wireless transceiver devices, including wireless communications devices (WCD""s) and other portable devices having a transceiver for wireless communication. One particular class of devices of finding applicability of the present invention includes portable laptop computers having a transceiver component for wireless communication. In one embodiment, the antenna structure according to the present invention is especially adapted for portable laptop computers and other portable wireless communication devices having an upper member, such as a cover, lid, clamshell, flip top, etc. and a lower member mechanically coupled to the upper member. The upper and lower member may be positioned in an xe2x80x9copenedxe2x80x9d state where the upper and lower members are oriented perpendicular to each other, or in a xe2x80x9cclosedxe2x80x9d state where the upper and lower members are generally parallel to each other. It is another aspect of the present invention to provide an antenna assembly in the upper member or the lower member or in each of said upper and lower member, if desired.
Preferably such a cover member contains additional components and/or circuitry related to the operation of the WCD such as a passive display or a interactive display or other controllable buttons, switches, or other features for operating and using the WCD, but practice of the present invention does not require any such additional components.
Furthermore, such cover members may be manually operated or may be operated from a remote location and may be automatically opened and/or closed upon the occurrence of one or more events, such a time-out by an internal or external timing signal or upon receipt of a signal or upon completion of one of more computational or control operations originated within, or received by, the WCD from another location over a wireless communication network.
The antenna system of the present invention is preferably disposed on a rear surface of an upper cover member of a WCD and thus provides maximum response to two orthogonal polarizations of a nominal RF data signal (e.g., horizontal or vertical) for two extreme positions of the upper member with respect to the lower member (e.g., open/closed). More preferably, two antenna members comprise a set of metal plate antennas disposed as depicted in FIG. 1, FIG. 4, FIG. 5A, and FIG. 5B to provide adequate electrical isolation between the two antenna members.
One object of the present invention is to overcome limitations of the prior art antenna systems for each WCD coupled to a wireless local area network.
Another object of the present invention is to provide an improved polarization diversity antenna system for a laptop computer coupled to a wireless LAN using an antenna assembly as taught, enabled, and depicted herein.
Another object of the present invention is to provide at least one of the two available antenna patterns that is maximally responsive to vertical polarization with the upper cover member of a laptop computer in both the open state and the closed state. Meeting this particular object of the present invention finds particular utility in the art due to the fact that vertical polarization omnidirectional antennas are frequently used in a wireless LAN environment.
The individual antennas used in one embodiment of the present invention are metal plate type antennas, disposed on the upper member and preferably mounted near an outer corner of the upper member. Optimum spacing between the two antennas in the antenna system of the present invention has been determined in order to provide near-omnidirectional antenna performance patterns (e.g., see FIGS. 6-13).
Yet another object of the present invention is to provide a low profile PIFA-edge antenna having two grounding legs between the planar conductive element and the ground plane element. The second grounding leg provides the present antenna with generally equivalent bandwidth characteristics as compared to other PIFA antennas having a single grounding leg, though with a substantially smaller distance between the planar conductor and the ground plane. Additionally, for a given height constraint the additional grounding leg may increase the bandwidth characteristic of an antenna.
Yet another aspect of the present invention provides a low profile PIFA edge-type antenna having a relatively small spacing between the planar conductive element and the ground plane element. The spacing between the planar conductive element and the ground plane may be approximately xc2xcxcex, significantly smaller than alternative PIFA antenna structures.
Other aspects and advantages of the invention as taught, enabled, and illustrated herein are readily ascertainable to those skilled in the art to which the present invention is directed, as well as insubstantial modifications or additions, all of the above of which falls clearly within the spirit and scope of the present invention as defined and specifically set forth in each individual claim appended hereto. The following drawings are intended to illustrate one or more embodiments of the present invention and are not intended to limit the scope and breadth of the invention hereof, which invention shall be as broad and shall reach all structures recited in the claims appended hereto and in reference to the whole of the disclosure hereof as understood by those of skill in the art of wireless technology generally, and the science and art of antenna and antenna system design, operation, and manufacture.